Horizontally disposed wellbores have been employed in growing numbers in recent years to access oil reservoirs not previously realistically producible. Where the formation is consolidated, relatively little is different from a vertical wellbore. Where the formation is unconsolidated however, and especially where there is water closely below the oil layer or gas closely above, horizontal wells are much more difficult to produce.
Pressure drop produced at the surface to pull oil out of the formation is at its highest at the heel of the horizontal well. In an unconsolidated well, this causes water coning and early breakthrough at the heel of the horizontal well. Such a breakthrough is a serious impediment to hydrocarbon recovery because once water has broken through at the heel, all production from the horizontal is contaminated in prior art systems. Contaminated oil is either forsaken or separated at the surface. Although separation methods and apparatuses have become very effective they still add expense to the production operation. Contamination always was and still remains undesirable. Zonal isolation has been attempted using external casing packers and open hole packers in conjunction with gravel packing techniques but the isolation of individual zones was not complete using this method and the difficulties inherent in horizontal unconsolidated formation wells have persisted.
Another inherent drawback to unconsolidated horizontal wells is that if there is no mechanism to filter the sand prior to being swept up the production tubing, a large amount of sand is conveyed through the production equipment effectively sand blasting and damaging the same. A consequent problem is that the borehole will continue to become larger as sand is pumped out. Cave-ins are common and over time the sand immediately surrounding the production tubing will plug off and necessitate some kind of remediation. This generally occurs before the well has been significantly depleted.
To overcome this latter problem the art has known to gravel pack the horizontal unconsolidated wells to filter out the sand and support the bore hole. As will be recognized by one of skill in the art, a gravel packing operation generally comprises running a screen in the hole and then pumping gravel therearound in known ways. While the gravel effectively alleviates the latter identified drawbacks, water coning and breakthrough are not alleviated and the horizontal well may still be effectively occluded by a water breakthrough.
Since prior attempts at enhancing productivity in horizontal wellbores have not been entirely successful, the art is still in need of a system capable of reliably and substantially controlling, monitoring and enhancing production from unconsolidated horizontal wellbores.
The above-identified drawbacks of the prior art are overcome or alleviated by the unconsolidated horizontal zonal isolation and control system disclosed herein.
The invention teaches a zonally isolated horizontal unconsolidated wellbore where packers are not employed on the outside of the basepipe but a reliable zonal isolation is still created. Zones are created by interspersing blank basepipe with slotted or otherwise xe2x80x9choledxe2x80x9d basepipe. The blank pipe is not completely blank but rather includes closeable ports therein at preselected intervals. Screens are employed over these ports and (as conventional) over the slotted basepipe. Upon gravel packing, a near 100% of pack is achieved over the blank pipe section because of the closeable ports. Only about 60% is achievable without the ports. With a full gravel pack of a preselected distance, i.e., the distance of the blank pipe, and the ports closed, isolation is assured with fluid produced for a bad zone being virtually completely prevented from migrating to the next zone. By shutting off production from the undesirable zone, then, through production string seals, only the desired fluid is produced.